I like these threads, no matter how many times they get re-hashed.
1) I want core mechanics designed to reduce my prep time as a DM. The more modular design of creature stat blocks over 2E was a vast improvement. Keep going.
2) I want either the average number or the average power of a character's magic items to be drastically slashed across the board. High level play feels less like controlling a heroic character, and more like controlling a vehicle for heroic loot. It's also a stumbling block for me as DM. We run a session light on strict "encounters" and focus more on mystery or whatever, if I award xp for non-encounter content, I mess up the wealth, and vice versa. At the very least, I'd like a three-way wealth-by-level and CR system showing appropriate wealth for low, mid, and high magic item games and X/Y/Z CR listings based on which you picked.
3) I want a lot less of the published materials to be tools for DMs rather than players. On average, DMs purchase more books and accessories than players, and quite a lot of them are a headache rather than a help since most are just chock full of more player options. I finally stopped buying them after 3.5 launched. We just play core.
4) Pretty please with sugar on top, adopt AU's spells readied/spell slots system. All the feel of Vancian magic, all the grit of a spell-point system.
That's all off the top of my head.